The present invention relates to a large scale integrated circuit, and more particularly to a high-density integrated semiconductor device constituted by a voltage converter circuit and miniaturized devices (devices with small dimension) which can keep up with a wide range of operating power-supply voltages and power supplies. More particularly a large scale integrated circuit is provided on a monolithic chip upon which are integrated a microcomputer, a logic circuit, a dynamic RAM (random access memory), a static RAM, a ROM (read-only memory), etc.
In recent years, many portable electronic machines have come onto the market such as a lap-top type personal computer, an electronic pocket notebook, portable electronic media machines such as a solid-state voice recorder which performs voice recording without using a magnetic medium, and a solid-state camera (electronic still camera) which performs image recording without using the magnetic medium. In order for these portable electronic machines to be widely popularized, it is indispensable to realize an ultra large scale integrated circuit (ULSI) which permits a battery based operation or an information (data) retention operation using a battery (battery back-up). On the other hand, there has been increased demand for a semiconductor disk, which can provide higher speed accessing than a magnetic disk, as a large-capacity-file memory system for implementing a computer with higher performance. This semiconductor disk requires a very large-capacity memory LSI which, using a battery, can access the information.
The ULSIs used for these applications must satisfy the following requirements:
(1) Operation in a wide range of operating power supply voltages (1-5.5 V). This requirement permits a one-chip ULSI to be adapted for many kinds of power supplies, including 5 V (which is a standard power supply voltage for the present TTL compatible digital LSI), 3.3. V (which is one candidate for the standard power supply voltage for the future TTL reversible digital LSI), 3-3.6 V (which is a typical output voltage of a primary cell of lithium, etc.), and 1.2 V (which is a typical output voltage of a secondary cell of cadmium and nickel), etc.
(2) Measures for a secular change or time-dependent fluctuation (for a short period or long period) in the power supply voltage. This requirement removes the fear of operation failure due to voltage fluctuation which would result from the change in the cell voltage and the switching of the power supply between the operation under a nominal condition and a battery back-up operation.
(3) Power reduction in the standard operation or the battery back-up operation. This requirement permits a small-sized battery to operate the ULSI for a long period.
(4) Reduction in a switching current. This requirement decreases voltage fluctuation caused by switching in the battery voltage, preventing operation failure.
One example of a microprocessor product which operates in a wide range of operating voltages is disclosed in the 4-bit Microprocessor Handbook, p. 148, published by NIPPON DENKI Co., Ltd. The product name is .mu.PD7507SC. The range of the power supply voltage in this microprocessor is 2.2-6.0 V. Information in a data memory (static RAM) is retained with a minimum voltage of 2 V. In this memory, the recommended voltage is generally 5 V for the operating power supply voltage and 2 V for the data retention.
An example of dynamic memory using battery back-up in which power consumption in data retention (refresh) is decreased is disclosed in IEEE, Journal of Solid-State Circuits, Vol. 23, No. 1, pp. 12-18, February 1988. The power supply voltage is 5 V for both nominal operation and data retention.
An example in which an external voltage is dropped to be supplied to an internal circuit is disclosed in U.S. Pat. No. 4,482,985.
An example of the battery back-up for a memory is disclosed in U.S. Pat. No. 4,539,660.
A technique for changing the plate voltage of a dynamic RAM is disclosed in Japanese Patent Publication No. 61-61479.
The battery back-up of a static RAM is disclosed in the catalogue published by Hitachi, Ltd., pp. 44-45.
The other relevant references and patent publications will be identified in the following description.